Coverage report does not include types-only TS files

[igordanchenko]

Describe the bug

Discussed in #6158

In some cases, the coverage report does not include types-only .ts files. One particular case is when the tested file uses a types-only .ts file, but the types are not exported from the package barrel file. The file is not included in the report even with all: true in coverage settings.

Reproduction

1. Open https://stackblitz.com/edit/vitest-v2-ts-coverage-bug-5s95pp?file=test%2Ffoo.test.ts
2. Download the sandbox to run the test locally
3. npm install
4. npm run test:run

Observe coverage report:

 % Coverage report from v8
----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------|---------|----------|---------|---------|-------------------
All files |     100 |      100 |     100 |     100 |                   
 foo.ts   |     100 |      100 |     100 |     100 |                   
 index.ts |     100 |      100 |     100 |     100 |                   
----------|---------|----------|---------|---------|-------------------

System Info

System:
    OS: macOS 14.5
    CPU: (12) x64 Intel(R) Core(TM) i7-8850H CPU @ 2.60GHz
    Memory: 578.00 MB / 32.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 20.15.1 - ~/.nvm/versions/node/v20.15.1/bin/node
    npm: 10.7.0 - ~/.nvm/versions/node/v20.15.1/bin/npm
  Browsers:
    Chrome: 126.0.6478.182
    Safari: 17.5
  npmPackages:
    @vitest/coverage-v8: latest => 2.0.3 
    @vitest/ui: latest => 2.0.3 
    vite: latest => 5.3.4 
    vitest: latest => 2.0.3

Used Package Manager

npm

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
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• The provided reproduction is a minimal reproducible example of the bug.

[AriPerkkio]

To summarize the bug here:

• Empty files (no runtime code, e.g. type-only) are shown in report when they are imported by test files. ✅
• Empty files are not shown in report when they are not imported by any test, picked by coverage.all ❌

This behavior is inconsistent. During #5457 the changes of #5328 should have been reverted. The #5457 implements type-only file detection in proper way while #5328 was mostly a work-around since good solution was not available back then.

This line needs to be removed and we need to make sure that the type-only files are shown properly in coverage report when they are picked by coverage.all. These files should not be shown as uncovered like they used to before previous fixes.

vitest/packages/coverage-v8/src/provider.ts

Lines 399 to 402 in 807a2cb

	// Ignore empty files, e.g. files that contain only typescript types and no runtime code
	if (source && stripLiteral(source).trim() === '') {
	return null
	}